Hi Patrick,
On 30 November 2017 at 12:47, Patrick Bellasi <[email protected]> wrote:
> Currently schedutil updates are triggered for the RT class using a single
> call place, which is part of the rt::update_curr_rt() used in:
>
> - dequeue_task_rt:
> but it does not make sense to set the schedutil's SCHED_CPUFREQ_RT in
> case the next task should not be an RT one
>
> - put_prev_task_rt:
> likewise, we set the SCHED_CPUFREQ_RT flag without knowing if required
> by the next task
>
> - pick_next_task_rt:
> likewise, the schedutil's SCHED_CPUFREQ_RT is set in case the prev task
> was RT, while we don't yet know if the next will be RT
>
> - task_tick_rt:
> that's the only really useful call, which can ramp up the frequency in
> case a RT task started its execution without a chance to order a
> frequency switch (e.g. because of the schedutil ratelimit)
>
> Apart from the last call in task_tick_rt, the others are at least useless.
> Thus, although being a simple solution, not all the call sites of that
> update_curr_rt() are interesting to trigger a frequency switch as well as
> some of the most interesting points are not covered by that call.
> For example, a task set to RT has to wait the next tick to get the
> frequency boost.
>
> This patch fixes these issues by placing explicitly the schedutils
> update calls in the only sensible places, which are:
> - when an RT task wakes up and it's enqueued in a CPU
> - when we actually pick a RT task for execution
> - at each tick time
> - when a task is set to be RT
>
> Signed-off-by: Patrick Bellasi <[email protected]>
> Reviewed-by: Dietmar Eggemann <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> Cc: Rafael J. Wysocki <[email protected]>
> Cc: Viresh Kumar <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
>
> ---
> Changes from v2:
> - rebased on v4.15-rc1
> - use cpufreq_update_util() instead of cpufreq_update_this_cpu()
>
> Change-Id: I3794615819270fe175cb118eef3f7edd61f602ba
> ---
> kernel/sched/rt.c | 15 ++++++++++++---
> 1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 4056c19ca3f0..6984032598a6 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -959,9 +959,6 @@ static void update_curr_rt(struct rq *rq)
> if (unlikely((s64)delta_exec <= 0))
> return;
>
> - /* Kick cpufreq (see the comment in kernel/sched/sched.h). */
> - cpufreq_update_util(rq, SCHED_CPUFREQ_RT);
> -
> schedstat_set(curr->se.statistics.exec_max,
> max(curr->se.statistics.exec_max, delta_exec));
>
> @@ -1327,6 +1324,9 @@ enqueue_task_rt(struct rq *rq, struct task_struct *p, int flags)
>
> if (!task_current(rq, p) && p->nr_cpus_allowed > 1)
> enqueue_pushable_task(rq, p);
> +
> + /* Kick cpufreq (see the comment in kernel/sched/sched.h). */
> + cpufreq_update_util(rq, SCHED_CPUFREQ_RT);
> }
>
> static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int flags)
> @@ -1564,6 +1564,9 @@ pick_next_task_rt(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
>
> p = _pick_next_task_rt(rq);
>
> + /* Kick cpufreq (see the comment in kernel/sched/sched.h). */
p is null when there is no rt task to pick.
You should test this condition before calling cpufreq_update_util
> + cpufreq_update_util(rq, SCHED_CPUFREQ_RT);
> +
> /* The running task is never eligible for pushing */
> dequeue_pushable_task(rq, p);
>
> @@ -2282,6 +2285,9 @@ static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued)
> {
> struct sched_rt_entity *rt_se = &p->rt;
>
> + /* Kick cpufreq (see the comment in kernel/sched/sched.h). */
> + cpufreq_update_util(rq, SCHED_CPUFREQ_RT);
> +
> update_curr_rt(rq);
>
> watchdog(rq, p);
> @@ -2317,6 +2323,9 @@ static void set_curr_task_rt(struct rq *rq)
>
> p->se.exec_start = rq_clock_task(rq);
>
> + /* Kick cpufreq (see the comment in kernel/sched/sched.h). */
> + cpufreq_update_util(rq, SCHED_CPUFREQ_RT);
Is this change linked to the "- when a task is set to be RT" in the
commit message ?
I can't see a situation where this is call without the previous one.
AFAICT, enqueue_task_rt will be called before each call to this
function
> +
> /* The running task is never eligible for pushing */
> dequeue_pushable_task(rq, p);
> }
> --
> 2.14.1
>
Hi Vincent,
On 06-Dec 10:39, Vincent Guittot wrote:
> Hi Patrick,
>
> On 30 November 2017 at 12:47, Patrick Bellasi <[email protected]> wrote:
[...]
> > static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int flags)
> > @@ -1564,6 +1564,9 @@ pick_next_task_rt(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
> >
> > p = _pick_next_task_rt(rq);
> >
> > + /* Kick cpufreq (see the comment in kernel/sched/sched.h). */
>
> p is null when there is no rt task to pick.
> You should test this condition before calling cpufreq_update_util
Mmm... for what I see, from the above function's implementation,
_pick_next_task_rt() is always returning a valid pointer to an RT
task.
The above call does a:
p->se.exec_start = rq_clock_task(rq);
right before returning, and there is also a BUG_ON(!rt_se) in the
previous RT tasks scanning loop.
Am I missing something?
> > + cpufreq_update_util(rq, SCHED_CPUFREQ_RT);
> > +
> > /* The running task is never eligible for pushing */
> > dequeue_pushable_task(rq, p);
[...]
> > @@ -2317,6 +2323,9 @@ static void set_curr_task_rt(struct rq *rq)
> >
> > p->se.exec_start = rq_clock_task(rq);
> >
> > + /* Kick cpufreq (see the comment in kernel/sched/sched.h). */
> > + cpufreq_update_util(rq, SCHED_CPUFREQ_RT);
>
> Is this change linked to the "- when a task is set to be RT" in the
> commit message ?
>
> I can't see a situation where this is call without the previous one.
> AFAICT, enqueue_task_rt will be called before each call to this
> function
Yeah, you right, in core.c the pattern seems to always be:
if (queued)
enqueue_task()
if (running)
set_curr_task()
I'll remove this chunk from the next version.
>
> > +
> > /* The running task is never eligible for pushing */
> > dequeue_pushable_task(rq, p);
> > }
Thanks for the review!
--
#include <best/regards.h>
Patrick Bellasi
On 6 December 2017 at 12:38, Patrick Bellasi <[email protected]> wrote:
> Hi Vincent,
>
> On 06-Dec 10:39, Vincent Guittot wrote:
>> Hi Patrick,
>>
>> On 30 November 2017 at 12:47, Patrick Bellasi <[email protected]> wrote:
>
> [...]
>
>> > static void dequeue_task_rt(struct rq *rq, struct task_struct *p, int flags)
>> > @@ -1564,6 +1564,9 @@ pick_next_task_rt(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
>> >
>> > p = _pick_next_task_rt(rq);
>> >
>> > + /* Kick cpufreq (see the comment in kernel/sched/sched.h). */
>>
>> p is null when there is no rt task to pick.
>> You should test this condition before calling cpufreq_update_util
>
> Mmm... for what I see, from the above function's implementation,
> _pick_next_task_rt() is always returning a valid pointer to an RT
> task.
>
> The above call does a:
>
> p->se.exec_start = rq_clock_task(rq);
>
> right before returning, and there is also a BUG_ON(!rt_se) in the
> previous RT tasks scanning loop.
>
> Am I missing something?
No you're right the return Null is done earlier if there is no task
>
>> > + cpufreq_update_util(rq, SCHED_CPUFREQ_RT);
>> > +
>> > /* The running task is never eligible for pushing */
>> > dequeue_pushable_task(rq, p);
>
> [...]
>
>> > @@ -2317,6 +2323,9 @@ static void set_curr_task_rt(struct rq *rq)
>> >
>> > p->se.exec_start = rq_clock_task(rq);
>> >
>> > + /* Kick cpufreq (see the comment in kernel/sched/sched.h). */
>> > + cpufreq_update_util(rq, SCHED_CPUFREQ_RT);
>>
>> Is this change linked to the "- when a task is set to be RT" in the
>> commit message ?
>>
>> I can't see a situation where this is call without the previous one.
>> AFAICT, enqueue_task_rt will be called before each call to this
>> function
>
> Yeah, you right, in core.c the pattern seems to always be:
>
> if (queued)
> enqueue_task()
> if (running)
> set_curr_task()
>
> I'll remove this chunk from the next version.
>
>>
>> > +
>> > /* The running task is never eligible for pushing */
>> > dequeue_pushable_task(rq, p);
>> > }
>
> Thanks for the review!
>
> --
> #include <best/regards.h>
>
> Patrick Bellasi